1. Field of the Invention
The invention defined and claimed herein relates to a process for preparing dinitrobenzophenones which comprises reacting benzene with ethylene in the presence of an alkylation catalyst to obtain an alkylation product containing unreacted benzene, ethylbenzene, polyethylbenzenes, 1,1-diphenylethane and heavier products, separating benzene, ethylbenzene and polyethylbenzenes from said alkylation product, recovering from the remainder of said alkylation product a fraction whose boiling points fall within the temperature range of about 260.degree. to about 290.degree. C., reacting said fraction with nitric acid at a temperature within the range of about 130.degree. to about 210.degree. C., wherein the molar ratio of nitric acid to said fraction is in the range of about 3:1 to about 8:1, and thereafter reacting the total resulting reaction product with nitric acid in oleum to obtain a nitration product predominating in dinitrobenzophenones.
2. Description of Prior Art
1,1-Diphenylethane (DPE) is a valuable hydrocarbon for conversion to benzophenone, which, in turn, can be converted to the corresponding nitro and amine derivatives. Unfortunately, there are no simple methods known for its preparation in high yield. Thus, Baeyer, Ber., VI, 223 (1873) attempted to prepare 1,1-diphenylethane by reacting paraldehyde with benzene in the presence of sulfuric acid, but obtained only a resinous material. Later, in Ber. VII, 1190 (1874), he isolated some 1,1-diphenylethane from a tarry reaction product in disappointingly low yield. Spilker et al., Ber., 65B, 1686 (1932), condensed benzene with styrene in the presence of sulfuric acid and obtained a 25 percent yield of 1,1-diphenylethane. Higher yields of the same product, from 40 to 50 percent, were obtained by Reichert et al., J. Am. Chem. Soc., 45, 3090 (1923) in the mercury-catalyzed condensation of benzene with acetylene in sulfuric acid. More recently, Baeyer et al. in Ber., 94, 1717 (1961) and Ber., 95, 1989, ( 1962), reacted benzene with acetylene in the presence of phosphoric acid which has been saturated with boron trifluoride to obtain 1,1-diphenylethane in 65 percent yield, as well as some polymeric substances.
It is known that the residue resulting from the alkylation of benzene with ethylene in the presence of an alkylation catalyst, which is available at fuel value from styrene manufacturers, contains substantial amounts of 1,1-diphenylethane. Unfortunately, because of the many compounds associated with the 1,1-diphenylethane in said residue, whose boiling points are close to 1,1-diphenylethane, even efficient fractional distillation of said residue results in a fraction containing only up to about 95 weight percent 1,1-diphenylethane. Because the remaining compounds in said fraction would then function as impurities, the use of said fraction as a 1,1-diphenylethane source for subsequent use would not suggest itself.
J. G. Schulz and A. Onopchenko have shown, however, in their Application Ser. No. 394,260, filed July 1, 1982, entitled Process for Preparing Benzophenone, and assigned to the same assignee as the present invention herein, that by subjecting the defined fraction to oxidation with nitric acid under well defined conditions of reaction they were able to obtain an oxidation product from which by distillation they were able to recover substantially pure benzophenone.